Lens deflection in the electro optical system of a cathode ray tube



y 1962 c. R. CORPEW LENS DEFLECTION IN THE ELECTRO OPTICAL SYSTEM OF A CATHODE RAY TUBE Filed Nov. 29, 1957 JONPZOU zOCUm EmQ WQQZQG JOQRZOU MO MUUDOW 405.20. 20- huw wm INVENTOR. cmsauss l2. COIZPEW. BY Mfiw United States Patent 3,035,19 LENS DEFLECTION IN THE ELECTRO OPTICAL SYSTEM OF A CATHODE RAY TUBE Charles R. Corpew, San Diego, Caiifi, assignor to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Filed Nov. 29, 1957, Ser. No. 699,779 3 Claims. (Cl. 313-78) This invention relates to lens deflection in the electro optical system of a cathode ray tube and more particularly, to the use of an electronic lens in the deflection part of the electro optical system.

In many applications of cathode ray tube use, the size of the tube and its neck extension is determined by the final angle of deflection of the electron beam necessary to illuminate the greatest possible area upon the screen of the tube. That is, if the neck of the tube is relatively short, the deflection angles are required to be large. If the neck is rather long, these deflection angles can become somewhat smaller. As the electron beam increases in speed on its path toward the screen, it becomes more difiicult to deflect accurately toward or away from the tubes axis. Therefore, considerable power requirements are normally needed to terminally deflect the beam at wide angles of deflection. The use of large amounts of power to obtain wide angles of deflection in the final deflection means presents problems of considerable magnitude and especially so where rapid deflections in the beam are desired.

These problems arise whether electromagnetic or electrostatic deflection is used. However, the situation that generally manifests the problem is when large electromagnetic coils having large control currents are used in finally deflecting the electron beam. The rapid fluctuations in the control current necessary for quick deflection of the beam creates a condition capable of permanently damaging the coils. Further, the time constant of large magnetic coils is normally too long to permit the desired rapid changes in wide angle deflections of the beam. When electrostatic means is used for final deflection of the beam, the large voltage differentials required to give wide angle deflection causes distortion of the beam to be excessive.

Another problem encountered in deflecting the beam from the axis of the electro optical system, is that it is necessary that the electron beam not have its cross section distorted. Therefore, when using electrostatic or electromagnetic deflection means, great care is required in placing the beam at the electrical center of the final deflection means. However, even at that, the cross section of electron beams deflected to maximum angles of a general bulb configuration will cause cross sectional distortion.

The present invention improves considerably the aforesaid difliculties by utilizing an additional electron lens placed generally in the area of intersection of the neck of the tube and the bulb portion. This effects a cross over the electron beams immediately in front of the lens and permits wide angle focusing of the beam on the screen. Thus, the final deflection means is required to provide only small deflections of the beam to the lens, and accordingly, permits smaller control currents or potentials to be used. The electronic lens is capable of seeing a shaped image, in accordance with its deflection by the final deflection means, and to focus the image on the screen with a deflection dependent upon the deflection of the image and the focal length of the electron lens. Thus, very Wide deflections of the beam are obtainable commensurate with the use of a short focal length electronic lens. Inasmuch as the control potential to the electronic lens is steady state, it is readily apparent ice that large deflection angles can be obtained without requiring the use of large fluctuating potentials or currents. Hence, the invention obviates the problem of the required use of large potentials or currents to obtain Wide deflection angles, and further permits the beams to be deflected to any angle including the maximum angle of deflection without distortion of the beams cross section. The invention may also be utilized to provide added flexibility in the control of the beam as the properties of an electron lens can be variably controlled through variations in its control potential or current, as is Well known in the art.

This invention is of particular value in the optical system of shaped beam tubes. Shaped beam tubes are those series of tubes in which an electron beam is shaped into a particular configuration by a stencil like cutout portion of a matrix. The cross section of the electron beam, being in that configuration, must then be deflected at various points in the tube toward or away from the optical axis of the tube. In its travel, the beam is subject, in many of these deflections, to slight distortions. Therefore, when a shaped beam, such as disclosed herein, is normally deflected to maximum angles by known final deflection means, distortions do occur at the greater deflection angles. The introduction of an additional lens system as exemplified by the present invention at or about the juncture of the neck of the bulb of the tube, will permit maximum deflection through the lens system by effecting short focal length cross over immediately in front of the lens. This permits presentation of a cross sectional beam image upon the screen, having a reduced distortion while still having wide angle deflection. Also, it is possible through use of this invention to effectively shorten the overall length of the cathode ray tube, as will be more readily apparent from the following description:

In addition to any objects and advantages aforestated, it is an object of the present invention to facilitate the use of a shortened cathode ray tube by utilizing an improved system of providing wide angle deflection of the electron beam.

Another object of this invention is to provide a cathode ray tube capable of. deflecting an electron beam through maximum final deflection angles in a substantially distortionless manner.

A further object of this invention is to provide a cathode ray tube capable of providing wide angle deflection of an electron beam through the use of an electronic lens.

Still another object of the present invention is to permit substantial reduction in the deflection angle normally necessitated by the final deflection system through the use of a lens capable of providing short cross over of the electron beam to permit a wide range of substantially distortionless deflection of the beam to maximum deflection angles permitted by screen size and bulb configuration.

Still a further object of the present invention is to provide a cathode ray tube capable of focusing an image of the cross section of the electron beam through a maximum desired final deflection angle, which cross sectional image is presented upon the screen substantially free of any distortions resulting from such final deflection.

Objects and advantages other than those set forth above will be apparent when read in connection with the accompanying specification and drawings, in which:

FIGURE 1 is the schematic view of a cathode ray tube embodying the instant invention;

FIGURE 2 is a view in detail of another embodiment of the invention in which electromagnetic lensing means are utilized;

FIGURE 3 is a schematic representation of a disadvantage encountered in prior art wide angle deflection systems;

FIGURE 4 is a schematic representation of how the invention provides wide angle deflection with substantially no distortion.

Shown in FIGURE 1 is a shaped beam tube having an evacuated envelope 10. Positioned at one end of the envelope is a beam generating and projecting means 11 capable of projecting an electron beam 16 substantially along the longitudinal axis of the tube 14 A conventional electron generating cathode 13, along with desired accelerating and focusing anodes 14, may be included in the beam generating means 11. A target 15, such as a phosphor screen, may be positioned at the other end of the tube 10 for electron to light conversion of the information to be displayed by a shaped electron beam 17.

In brief, the operation of the tube is as follows. An electron beam is projected by the projecting means 11 to electrostatic selection plates 19, which select which character in matrix 18 the beam will contact causing a distinctively shaped beam 17. The path of travel of beam 17 is redirected by convergence coil 20 so that its path is substantially along the longitudinal axis of the tube. Also, coil 20 focuses the shaped character of the beam to an image in a two dimensional image zone 24. Positioning means, including final deflection means 23 and lens 25, positions the beam on the screen. Final deflection means 23 deflects the shaped beam to a desired point in lens 25 thus, placing the imaged character at a predetermined point along the image line 24. Lens 25 sees the shaped character of the beam at its point along the image line 24, and images the character in focus on screen 15. Since lens 25 has a short focal length and is of the convergence type, it crosses over the beam at a point 26 close to the 'lens and provides wide deflection of the beam to the screen.

In a more detailed description of the invention with reference to FIGURE 1, the electron beam 16 may be shaped into a predetermined character cross section or configuration by a beam shaping member 13 positioned along the axis intermediate target 15 and beam generating means 11, resulting in the shaped electron beam 17. Shaped electron beam 17 acquires the cross sectional shape imparted to the beam 16 by a stencil like opening or object in beam shaping member 18. A selection deflection means 19, which may be of the electromagnetic or electrostatic construction, is shown in the exemplification as two pairs of electrostatic deflection plates placed in quadrature with each other. The selection deflection means 19 is capable of deflecting beam 16 to the desired character of shaping member 18. This illuminates the character object opening or portion of the beam shaping member 18, thus, giving the desired shaped beam 17.

Convergence means 25 which may be of an electrostatic or electromagnetic construction, is shown in the instant exemplification as electromagnetic and is utilized to effect a converging of the divergent electron beam 17 to the longitudinal axis of the tube. Along with its convergence eflect, converging means effects substantially simultaneously a focusing action of the shaped beam 17 whereby the character illuminated in the beam shaping member 18 is imaged at a desired imaging point 24. Convergence means 26, therefore, effects a redirection of the divergent shaped electron beam 17 and presents the beam 17 on a path converging with the longitudinal axis to the final deflection means 23. The final deflection means serves to deflect the beam to the electron convergence lens and comprises electrostatic plates which may have horizontal plates split into two portions permitting deflection of the beam in a manner as illustrated and described in United States Patent No. 2,811,668, issued October 29, 1957, to Joseph T. McNaney and assigned to the same assignee as the present application. This electrostatic plate arrangement permits deflection of the electron beam 17 to lens 25 in substantially a distortion free manner, even though beam 17 in its path from con- 4 vergence means 2% may not be moving in a direction exactly parallel with the longitudinal axis of the tube, at the time of entering deflection control unit 23. The amount of deflection applied to the beam by deflection means '23 is dependent upon the predetermined signals received from the deflection control unit, which generally establishes a deflection commensurate with that required to deflect the beam to a point in the electron lens 25 giv ing the desired cross over of the beam to the screen. I

Lens action 25 is illustrated in phantom in FIGURE 1; This lens action is created by electrostatic lens 31, which is illustrated as a three-element Einzel lens. FIGURE 2 illustrates a sectional view of FIGURE 1, wherein an electromagnetic focusing coil 28 is used. The coil is char acterized by having its gap made very small and brought as close to the axis of the tube as possible by pole pieces 22. The particular types of electrostatic and electromagnetic focusing means illustrated in FIGURES 1 and 2 are disclosed only for purposes of this specific embodiment. It is to be understood that any type of electronic lens, capable of providing a thin lens action, may be used. Both of the electrostatic and electromagnetic lens illus trated are well known in the art. Generally, the electro-' static type lens is preferred over electromagnetic as their power requirements are smaller and the field they generate is capable of being adequately controlled free of interference with the adjoining fields. While lens 25 is normally controlled by steady state current or voltage, application of independently variable control voltages or currents to the lens 25 will permit independent variation of the imaging distance and the cross sectional size of beam 17, as will be explained in greater detail later.

Lens 25 serves to focus image 24 in an inverted display on screen 15 having an increased magnification. Thus, lens 25 must be positioned in correct distance relationship with respect to image 24 and screen 15, thereby permitting image 24 to be focused onto screen 15. As lens 25 serves merely to re-image, image 24 on screen 15, -it is apparent that the shorter the focal length of lens 25, the closer cross over point 26 will be to lens 25 and accordingly, the wider the angle of deflection of shaped beam 17 to the screen and the shorter the overall length of the tube.

In the operation of shaped beam tubes, the shaped beam image is normally focused on screen 15 by the convergence lens 20. However, in the present invention, it is required that an image be focused at point 24 rather than on screen 15, therefore, new distance relationships must be established between the various components of the tube to permit an image to be focused at image point 24. As shown in FIGURE 1, the established distance, for the specific embodiment illustrated, between selection means 19 and deflection means 23 is four focal lengths. The center of convergence lens 20 being positioned equidistant (two focal lengths) between deflection control unit 23 and deflection control unit 19. The matrix is set focal length from selection control 19 and 1 /2 focal lengths from convergence lens 20. The latter 1 /2 focal lengths being the object distance Q By the application of well known image optical formulas, it may be established that with this relationship, the image distance Q will be three focal lengths from the center of convergence lens 20. These parameters, for the specific embodiment, provide that the image 24 will be twice the size of the characters in matrix 18. This image size at image point 24 may be varied as desired by changing the ratio of Q to Q or the object distance to the imaged distance. It is generally desired that the image size of image 24 be small in view of the high magnification of the thin lens element 25.

The magnification of shaped beam 17 by thin lens 25 depends upon the ratio of the object to lens distance a to the lens to image distance b. Thus, if distance a is 1 and distance b is 5, the magnification provided by lens 25 will then be 5, and the shaped beam character 17 illustrated on the screen 15 will be 5 times the size of alt.

the character imaged at point 24. Thus, if the image 24 is twice the size of the matrix characters at matrix 18, then the final image on the screen will be ten times the size of the matrix character of the matrix 18. The magnification of lens 25 may be varied by varying the control current or potential to coil 28 or electrostatic lens 31 in FIGURE 2. However, if the magnification of lens 25 is varied, then it will generally be desirable that the electromagnetic coil 28 or electrostatic lens 31 be moved axially within the tube thereby realigning the ratio of the image to object distance a and b and permitting focusing of the beam under the new conditions. This provides flexibility in varying the size of the image on the screen as well as its degree of wide angle deflection.

The ability of the electron lens arrangement to provide substantially distortion free focusing of image 24 on screen 15, even though wide angle deflection of the beam is obtained, may be attributed to several reasons. One of which is that electrostatic or electromagnetic deflection apparatus do not have completely uniform fields and thii is especially so when the field intensity is large. There fore, when wide angle deflection is obtained by electro static or electromagnetic deflection means alone, high intensity fields are required which increases the distortion of the beam. With smaller angles of deflection, however, there is less distortion of the beam. This inven tion requires that the beam be deflected only a small amount to lens 25, thereby presenting an image 24 to lens 25 that is relatively free of distortion.

FIGURES 3 and 4 illustrate diagrammatically the ability exhibited by electronic lens 25 in focusing image 24 onto the screen at wide angles with substantially no distortion. With respect to FIGURE 3 which discloses the prior art method of providing wide angle deflection, the beam is deflected from the longitudinal axis 29 of a tube to the screen represented by line 31 from a point 36 in the final deflection means. The beam 32 is in the shape of a circle 34 and Will strike the screen 31 at point 35 at the angle as shown. This angular striking of the beam against screen 31 gives an oval image 36. Dotted line 33 represents where the line of contact with the screen would have to be to cause a completely circular beam to be illustrated. FIGURE 4 shows how the shaped beam is illustrated in true representation on the screen through the use of a thin lens as is illustrative of this invention. The beam is deflected from the longitudinal axis 43 at point 37 by a deflection means. The beam has the shape of a circle 38, and is deflected to the point of convergence of lens 40. The beam forms an image 39 which is picked up by lens 40 crossed over at point 41 and illustrated on screen 42 as a distortion-free circle 44. This follows because the lens merely re-images the image 39 onto screen 42. Therefore, since circle 38 is a part of image 39, it is focused onto screen 42 without distortion regardless of the fact that screen 42 receives the beam 41 at an angle.

Lens 25 is also capable of providing an added control of the beam supplementary to convergence coil 20, thus, the length of the tube is not determinative by the distance required by coil 20 to focus an image upon screen 15.

The particular embodiment of the invention illustrated and described herein is illustrative only and the invention includes such other modifications and equivalents as may readily appear to those skilled in the art, within the scope of the appended claims.

I claim:

1. A shaped beam cathode ray tube capable of producing undistorted large size presentations without using large deflection angles, or powerful deflecting circuitry and power-consuming deflection systems, comprising: an evacuated cathode ray tube envelope having a faceplate; means, positioned in said tube, for producing an electron stream; a matrix having character-shaped apertures, positioned in the path of said electron stream; means for directing said electron stream toward selected portions of said matrix whereby electrons traversing said apertures emerge as a shaped electron beam whose cross section corresponds to the shape of said traversed aperture; electron optical means for converging said shaped electron beam at a crossover point and forming an image of said character-shaped apertures in an image plane; means, comprising a low-powered, small-angle deflection system positioned to straddle said crossover point, for causing the image of selected character-shaped apertures to be selectively positioned in said image plane to form a display; and means, comprising a fixed-strength symmetrical electron lens positioned between said deflec tion system and said faceplate, for converting said display in said image plane into a larger presentation on said faceplate.

2. A shaped beam cathode ray tube capable of producing undistorted large size presentations without using large deflection angles or powerful deflecting circuitry and power consuming deflection systems comprising: an evacuated cathode ray tube envelope having a faceplate; means for producing a shaped electron beam; electron optical means for converging said shaped electron beam at a crossover point and forming an image in an image plane; means, comprising a low-powered, small-angle deflection system positioned to straddle said crossover point, for causing the image produced by said shaped electron beam to be selectively positioned in said image planewhereby selected said images form a display in said image plane; and electron lens means, positioned between said deflection system and said faceplate, for converting said display on said image plane into a large presentation on said faceplate.

3. A shaped beam cathode ray tube capable of producing undistorted large size presentations Without using large deflection angles or powerful deflecting circuitry and power consuming deflection systems comprising: an evacuated cathode ray tube envelope having a faceplate; means for producing an electron beam; electron optical means for converging said electron beam at a crossover point; means, comprising a low-powered, small-angle deflection system, for causing said electron beam to produce a display in an image plane; and electron lens means, positioned between said deflection system and said faceplate, for converting said display in said image plane into a large presentation on said faceplate.

References Cited in the file of this patent UNiTED STATES PATENTS 2,058,914 Rudenberg Oct. 27, 1936 2,218,702 Diels Oct. 22, 1940 2,237,651 .Bruche Apr. 8, 1941 2,259,099 Bernamont Oct. 14, 1941 2,452,919 Gabor Nov. 2, 1948 2,467,009 Bull Apr. 12, 1949 2,515,926 Le Poole July 18, 1950 2,541,446 Trott Feb. 13, 1951 2,769,116 Koda Oct. 30, 1956 2,839,679 Harris June 17, 1958 2,892,962 Ross June 30, 1959 2,944,174 Taylor July 5, 1960 FOREIGN PATENTS 109,216 Sweden Dec. 7, 1943 402,287 "Italy Feb. 26, 1943 938,862 Germany Feb. 9, 1956 

